I have never seen a position description that did not include something along the lines of "and other duties as required".

It doesn't matter that it is another department. I think that is what is getting people riled up at you. It doesn't matter if they ask you to sweep the front pavement, go and do it. Someone has to go do that job, you were asked, go do it. If it doesn't get done, and customers are not happy, then business is not good, business not good, they need to fire people, people who are not willing to help the company in whatever capacity they were asked to help out in will be fired first.